1. Field of the Invention
The subject invention is directed to fuel injection, and more particularly, to a system and method for cooling the exit slots of the main fuel circuit of a staged airblast fuel injector using the pilot fuel flow, at low engine power.
2. Background of the Related Art
Staged fuel injectors for gas turbine engines are well know in the art. They typically include a pilot fuel atomizer for use during engine ignition and low power engine operation and at least one main fuel atomizer for use during high power engine operation in concert with the pilot fuel atomizer. One difficulty associated with operating a staged fuel injector is that when the pilot fuel circuit is operating alone during low power operation, stagnant fuel located within the main fuel circuit can be susceptible to carbon formation or coking due to the temperatures associated with the operating environment. This can degrade engine performance over time.
In the past, attempts were made to passively insulate or otherwise protect the main fuel circuit of a staged fuel injector from carbon formation during low power engine operation using heat shields or vents. Efforts have also been made to actively cool a staged fuel injector using fuel flow from the pilot fuel circuit. One such effort is disclosed in U.S. Pat. No. 5,570,580 to Mains, which provides a fuel injector having two dual orifice injector tips, each with a primary and secondary pressure atomizer. There, fuel streams to the primary and secondary sprays of the pilot and main nozzle tips are arranged to transfer heat between the pilot primary fuel stream and each of the main secondary fuel stream and the pilot secondary fuel stream.
To date however, active cooling has not been used to protect against carbon formation in the main fuel circuit of a staged airblast fuel injector. Accordingly, there is a need in the art for a method of actively cooling a staged piloted air blast or dual prefilming pure airblast fuel injector to prevent carbon formation or coking in the main fuel circuit during low power engine operation and in general, to enable the pilot fuel flow to cool the main fuel circuit during high power engine operation, so as to enhance the engine performance and injector life.